混合型MMC非闭锁型直流故障穿越的故障等效模型

由半桥子模块和全桥子模块构成的混合型MMC相比全桥型MMC能够在降低成本的同时具备直流故障穿越能力，直流故障暂态分析是混合型MMC器件选型和配比设计的基础。为分析混合型MMC直流侧故障的暂态特性，建立了额定运行状态下和降压运行状态下发生极间短路的混合型MMC非闭锁型直流故障穿越过程的故障等效模型，分析了直流故障穿越期间混合型MMC各桥臂子模块的动态投切过程，将非闭锁型直流故障穿越控制策略切换前的暂态过程等效为不可控的子模块电容放电过程，将控制策略切换后的暂态过程等效为带有电感初始储能和反向电压源的限流过程，并给出了直流侧短路电流的解析计算方法。最后，基于PSCAD/EMTDC搭建仿真模型，验证了本文所提模型和计算方法的有效性，能够为混合型MMC的优化设计提供参考。

Fault equivalent model for non-blocking DC fault ride-through of hybrid MMC

Compared with full-bridge MMC, the hybrid MMC composed of half bridge sub-module and full bridge sub-module can reduce the cost and have the DC fault ride-through capability. The DC fault transient analysis is the basis of device selection and proportioning design of hybrid MMC. In order to analyze the transient characteristics of hybrid MMC after DC side fault, the equivalent fault models of DC pole-pole short circuit during the non-blocking DC fault ride-through in rated operation and step-down operation are established, and the dynamic switching process of each bridge arm sub-module of hybrid MMC during DC fault ride-through is analyzed. The transient process before the switching of the non-blocking DC fault ride-through control strategy is equivalent to the uncontrollable sub-module capacitor discharge process, while the transient process after the control strategy is switched is equivalent to the current limiting process with the initial energy storage of the inductor and the reverse voltage source. And the analytical calculation method of the short-circuit current on the DC side of the hybrid MMC is given in this paper. Finally, the effectiveness of the model and calculation method proposed in this paper are verified by the PSCAD/EMTDC simulation platform, which can provide a reference for the optimal design of hybrid MMC.